The present invention relates to an exhaust gas recirculation (EGR) controller for recirculating some of exhaust gas to combustion chambers of an internal combustion engine.
When an anomaly in fuel injection is detected in a typical internal combustion engine, fail control is performed to cope with the anomaly. For example, Japanese Laid-Open Patent Publication No.10-299557 describes that operation of an internal combustion engine is immediately interrupted when too much fuel is injected from a fuel injection valve. Further, the publication describes that when the appropriate fuel injection pressure cannot be obtained due to a fuel pump anomaly or a clogged filter, it is preferable that the internal combustion engine continue to operate in an engine safety mode.
Internal combustion engines include so-called port injection engines, which inject fuel into an intake port, and so-called direct injection engines, which inject fuel into combustion chambers. Injected fuel is difficult to vaporize when the engine temperature is still low, for example, when starting the engine. Fuel vaporization is more difficult in port injection engines than in direct injection engines.
In order to enhance the vaporization of injected fuel, for example, the period during which an intake valve and an exhaust valve are both simultaneously open (valve overlap period) is set longer during cold operation of the internal combustion engine than during normal operation. This increases the amount of exhaust gas returned from an exhaust passage to a combustion chamber and raises the temperature in the combustion chamber with the heat of the EGR gas. As a result, the vaporization of the injected fuel is enhanced. By drawing EGR gas into the combustion chamber, fuel vaporization is enhanced and a relatively satisfactory combustion condition is maintained even when fuel is directly injected into a combustion chamber during cold operation.
When the fuel injection pressure is low, relatively large fuel droplets are injected. Such large fuel droplets are difficult to vaporize. If some of exhaust gas is returned (recirculated) to the combustion chamber when the fuel injection pressure is low, the recirculated gas (EGR gas) would enhance the vaporization of the fuel droplets. However, the proportion of the amount of fresh air (oxygen) required for combustion in the combustion chamber would decrease. This would deteriorate combustion in the combustion chamber. As a result, misfire or engine speed fluctuation may occur.
This problem is particularly noticeable in direct injection engines but also arises in port injection engines. Further, this problem occurs not only in an engine provided with an internal EGR function, in which EGR gas is drawn into the combustion chamber by prolonging the valve overlap period, but also occurs in an engine provided with an external EGR function, in which some of exhaust gas in an exhaust passage is returned to an intake passage through an EGR pipe connecting the exhaust passage to the intake passage.